Process for the preparation of a copolymerizable composition.
The invention relates to a process for the preparation of a copolymerizable composition and to a process for the preparation of a peroxide composition to be used in the copolymerization of said copolymerizable composition.
By unsaturated polyester resins are to be understood solutions of unsaturated polyesters in reactive monomers and one or more polymerizable CH.sub.2 .dbd.C&lt; groups such as styrene, vinyl toluene, methyl methacrylate, diallyl phthalate and divinyl benzene.
The ratio monomer to unsaturated polyester is generally 30-50% by weight of monomer to 70-50% by weight of polyester.
The unsaturated polyester is obtained by reaction of approximately equivalent amounts of a polyvalent alcohol such as ethylene glycol, propylene glycol, diethylene glycol and an unsaturated dibasic carboxy acid such as maleic acid, fumaric acid, itaconic acid in the presence, if desired, of a saturated acid such as phthalic acid, isophthalic acid, tetrachlorophthalic acid, malonic acid, adipinic acid, sebacinic acid, succinic acid and the like.
In order to improve the stability of the unsaturated polyester, inhibitors are incorporated in them in amounts ranging from 0.001 to 0.003% by weight. The most commonly used inhibitors are hydroquinone, quinone and para tert. butyl catechol.
The above-described unsaturated polyester resins may be copolymerized at room temperature under the influence of organic peroxides yielding free radicals and in the presence of one or more accelerators for the peroxide used.
The British patent specification No. 954,600 describes the use of particular aldehyde peroxides as initiators in combination with a cobalt compound and a secondary amine in the copolymerization of unsaturated polyester resins at room temperature.
These aldehyde peroxides are obtained by condensation of an aldehyde with hydrogen peroxide under reaction conditions which are not specified. The impression is given, however, that the reaction must be so conducted that the condensation product preferably contains 1-hydroxy-1-alkylhydroperoxide and bis(1-hydroxy alkyl) peroxide. These peroxides may be regarded as aldehyde peroxides which contain respectively 1 active oxygen atom and 1/2 active oxygen atom per carbonyl group of the aldehyde used in the preparation of the peroxide. It is recommended that in practice the copolymerization of unsaturated polyester resins should be carried out using a combination of bis(1-hydroxy heptyl) peroxide and a cobalt accelerator. Unsaturated polyester resins in which such a combination is incorporated have a short gel time, which meets with practical drawbacks.